I am surprised how often this question comes up in writing chat groups. People say they have a work that is so-many-thousands of words, and they want to know if it counts as a story. In some way, I understand what they are asking, but in other ways, I think they are missing the greater question. Let's clarify the first part a little, then dive into the second part.
Less than 10,000 words: Short story
10,000-50,000 words: Novella
More than 50,000 words: Novel
(greater than 300,000 words: Too long)
This is really little more than just definition, and doesn't matter until you are talking to a potential publisher and they have their own standard of so many words for a publication. Numerous short story publishers have different standards for what they will consider. Hemingway famously boasted of writing a story six words long. And yes, I know of someone who wrote a "modest" novel that was over 300,000 words (it has not yet been published). However, don't let the definition take you away from the task of writing a story. That is a different thing altogether.
When we write a story, we generally have an idea of a character or characters, the journey they go on, the obstacles they face, how the mission is completed, and what life is like afterwards. These are the ingredients for a story - not the length of the work. In this regard, our obligation as writers is to make sure we make all those steps as complete and satisfying as possible to our reader, and give them a full experience of what might be an otherwise simple journey.
When a lot of writers first start out, they want to write the complete story of the hero's journey. They introduce the main character, lay out the problem, send them on the mission, it gets completed, and we're done. That, technically, is the complete story. However, it is quite boring. It is not engaging. Part of the mission of telling the hero's story is storytelling - making that person full and real. Before the hero runs off on their mission, the reader needs to know about them. Their habits, their interests; the things that connect the hero to the life of the reader. Rushing to the mission is one thing, but if the hero gets a cup of coffee with too much cream, the reader connects with this point and relates to their situation through that cup of coffee. It's extra words, but it benefits the story.
A lot of words in a story come from the conversations, the descriptions, the narrative that shapes the world around the hero. When those words are used in a way that helps the reader, the story gets better. It becomes a longer work, but the reward is even greater.
The main takeaway is to not be concerned about the length of the story. Focus on your engagement with the reader, how you want your words to affect them, and the journey you wish to take them on. If you want to share a quick little event with a sharp twist at the end, write it and call it a short story. If you want to transport your reader to a different place and time, focus on the description and world-building, and let the novel create itself.
And if it is in excess of 300,000 words, get some outside input. It's too long.